Magnetoresistive random access memory (MRAM) is now a proven nonvolatile memory technology with many advantages over other commercialized memory types in areas such as write/read speed, power consumption, lifetime, etc. However, conventional MRAM has a fundamental limitation of scalability. In a newer design of MRAM, a spin transfer switching technique (STT) can be used to manipulate the memory element as well. This new design will allow better packing and shrinkage of individual magnetic tunneling junction (MTJ) devices on the wafer, effectively increasing the overall density of the MRAM memory elements. STT MRAM not only possesses the major benefits of conventional MRAM but also has tremendous potential for scalability. Unlike conventional MRAM that requires a separated word line in addition to a BIT line to switch the magnetization direction of the free layer (FL), STT MRAM relies on only a current passing through a MTJ junction to rotate the magnetization direction of the free layer (FL). In order for STT MRAM to switch a bit, however, the current density passing through the MTJ device should be larger than a critical switching current density (Jc). Since current density is inversely proportional to device physical size given a fixed amount of current, the switching efficiency increases as the critical dimension (CD) size of MTJ junction decreases. Thus, CD is normally very small for STT MRAM (typically <100 nm). In our previous disclosures (U.S. Pat. No. 7,884,433, U.S. Pat. No. 8,133,745, and U.S. patent application Ser. No. 12/586,900), all incorporated herein in their entirety, we revealed our methods to address many challenges for STT memory device fabrication.
MRAM devices are often combined with complementary metal-oxide-semiconductor (CMOS) devices. Process integration involves connection between MRAM and CMOS elements without causing any defect related issues.
U.S. Patent Application 2007/0069296 to Park et al describes a deep via contact from CMOS to MRAM. U.S. Pat. No. 7,999,246 to Iwayama and U.S. Patent Application 2008/0089118 to Kajiyima show ring-shaped magnetic junction elements.